Ship-to Party is not maintained in sales area

Hi,

While creating a sales order for a company code and if we give a different ship-to party, which is not belongs to that sales area, I'm getting a message "Ship-to Part XXX is not maintained in sales area abc xxxx yy zz".

When I tried to add one more partner at header level, say "Mark for customer", and give the different customer number, the error is not coming.

Can anyone tell whether this check will be done only for standard partners like Sold-to, Ship-to etc? and not for custom partners?

Thanks,

Kishore